Mac OS builds failing re OpenMP

[weshinsley]

Something has changed in github CI for Mac OS -

-- The C compiler identification is AppleClang 14.0.0.14000029
-- The CXX compiler identification is AppleClang 14.0.0.14000029
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode_14.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode_14.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Setting build type to 'RelWithDebInfo' as none was specified.
CMake Error at /usr/local/Cellar/cmake/3.25.1/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find OpenMP_C (missing: OpenMP_C_FLAGS OpenMP_C_LIB_NAMES)
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.25.1/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:600 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/Cellar/cmake/3.25.1/share/cmake/Modules/FindOpenMP.cmake:580 (find_package_handle_standard_args)
  CMakeLists.txt:35 (find_package)

Adding this section in the root CMakeLists.txt:

  # Find OpenMP
if(APPLE AND USE_OPENMP)
    if(CMAKE_C_COMPILER_ID MATCHES "Clang")
        set(OpenMP_C "${CMAKE_C_COMPILER}")
        set(OpenMP_C_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
        set(OpenMP_C_LIB_NAMES "libomp" "libgomp" "libiomp5")
        set(OpenMP_libomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libgomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libiomp5_LIBRARY ${OpenMP_C_LIB_NAMES})
    endif()
    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
      set(OpenMP_CXX "${CMAKE_CXX_COMPILER}")
      set(OpenMP_CXX_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
      set(OpenMP_CXX_LIB_NAMES "libomp" "libgomp" "libiomp5")
      set(OpenMP_libomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
      set(OpenMP_libgomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
      set(OpenMP_libiomp5_LIBRARY ${OpenMP_CXX_LIB_NAMES})
    endif()
endif()

seems to be part of the answer - we get passed the configure stage, but fail when building with:

 [  2%] Building CXX object src/Geometry/CMakeFiles/geometrylib.dir/Vector2.cpp.o
[  4%] Linking CXX static library libgeometrylib.a
[  4%] Built target geometrylib
[  6%] Building CXX object src/CMakeFiles/CovidSim.dir/CovidSim.cpp.o
clang: error: unsupported argument 'libomp' to option 'fopenmp='
make[2]: *** [src/CMakeFiles/CovidSim.dir/CovidSim.cpp.o] Error 1
make[1]: *** [src/CMakeFiles/CovidSim.dir/all] Error 2
make: *** [all] Error 2

and removing the libomp from the fopenmp= fails with

 [  6%] Building CXX object src/CMakeFiles/CovidSim.dir/CovidSim.cpp.o
clang: error: unsupported option '-fopenmp'
make[2]: *** [src/CMakeFiles/CovidSim.dir/CovidSim.cpp.o] Error 1
make[1]: *** [src/CMakeFiles/CovidSim.dir/all] Error 2
make: *** [all] Error 2

[weshinsley]

So - something has changed in the Mac OS images github uses, and I think there is some sort of conflict between different versions of Clang/C++ that seem to coexist. Logging into the CI node and running clang --help shows that -fopenmp should be possible, but at the build it seems to be an invalid option. I've worked around this for now by disabling OpenMP support and only running the single-threaded tests on Mac OS. Not an ideal solution, but Apple seem to be making this hard, and I'm out of ideas for now.

Having fixed that, google-tests 1.10 would also no longer compile on the Mac OS image, because of some deprecations that are now viewed by Apple's compiler as fatal errors. A bit of a balancing act:-

• The Centos 7 image will compile 1.10, but nothing more recent.
• Mac OS will compile 1.11 onwards.
• Other linux builds are failing to compile the recent 1.13 at present.

So I've moved Google Tests to the 1.12.1 release and if CentOS is detected, fall back to 1.10.

[weshinsley]

If anyone should read this and know how to fix OpenMP on the Mac OS build, I would be very grateful for advice!

[weshinsley]

Bit more progress -

if(APPLE)
  set(CMAKE_C_COMPILER "/usr/local/opt/llvm/bin/clang")
  set(CMAKE_CXX_COMPILER "/usr/local/opt/llvm/bin/clang++")
  add_compile_options("-I/usr/local/opt/libomp/include -L/usr/local/opt/libomp/lib")
  link_libraries("-I/usr/local/opt/libomp/include -L/usr/local/opt/libomp/lib")
endif()

Pasting this before the project line successfully forces the compiler to be the right one. We then get an error later on (this is verbose from cmake --build . -v)

[  6%] Linking CXX executable CovidSim
cd /Users/runner/work/covid-sim/covid-sim/build/src && /usr/local/Cellar/cmake/3.25.2/bin/cmake -E cmake_link_script CMakeFiles/CovidSim.dir/link.txt --verbose=1
/usr/local/opt/llvm/bin/clang++ -O2 -g -DNDEBUG -isysroot /Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk -mmacosx-version-min=12.6 -Wl,-search_paths_first -Wl,-headerpad_max_install_names CMakeFiles/CovidSim.dir/CovidSim.cpp.o CMakeFiles/CovidSim.dir/Rand.cpp.o CMakeFiles/CovidSim.dir/Error.cpp.o CMakeFiles/CovidSim.dir/Dist.cpp.o CMakeFiles/CovidSim.dir/Kernels.cpp.o CMakeFiles/CovidSim.dir/Bitmap.cpp.o CMakeFiles/CovidSim.dir/SetupModel.cpp.o CMakeFiles/CovidSim.dir/CalcInfSusc.cpp.o CMakeFiles/CovidSim.dir/Sweep.cpp.o CMakeFiles/CovidSim.dir/Update.cpp.o CMakeFiles/CovidSim.dir/Param.cpp.o CMakeFiles/CovidSim.dir/Person.cpp.o CMakeFiles/CovidSim.dir/Direction.cpp.o CMakeFiles/CovidSim.dir/InverseCdf.cpp.o CMakeFiles/CovidSim.dir/Memory.cpp.o CMakeFiles/CovidSim.dir/CLI.cpp.o CMakeFiles/CovidSim.dir/Files.cpp.o CMakeFiles/CovidSim.dir/ReadParams.cpp.o -o CovidSim  -I/usr/local/opt/libomp/include -L/usr/local/opt/libomp/lib Geometry/libgeometrylib.a -I/usr/local/opt/libomp/include -L/usr/local/opt/libomp/lib -llibomp -llibgomp -llibiomp5 -llibomp -llibgomp -llibiomp5 
ld: library not found for -llibomp

So the -L and -I are there (twice as it happens), libomp.a and libomp.dylib are present in /usr/local/opt/libomp/lib (and similarly the include folder exists with .h files). So this looks promising, but still isn't right.

[weshinsley]

Ok - it turns out this is sufficient

if(APPLE)
  set(CMAKE_C_COMPILER "/usr/local/opt/llvm/bin/clang")
  set(CMAKE_CXX_COMPILER "/usr/local/opt/llvm/bin/clang++")
endif()

before the project line - don't specify the libraries - and everything will be picked up. The Google Test update (and backward-compatibility for CentOS) is still required with the compiler above.